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9 Jul 2012

Volume 101, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 023101 (2012); http://dx.doi.org/10.1063/1.4731792 (4 pages)

Feng Wang, Ayan Chakrabarty, Fred Minkowski, Kai Sun, and Qi-Huo Wei
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Ga1−xMnxN epitaxial films with high magnetization

G. Kunert, S. Dobkowska, Tian Li, H. Reuther, C. Kruse, S. Figge, R. Jakiela, A. Bonanni, J. Grenzer, W. Stefanowicz, J. von Borany, M. Sawicki, T. Dietl, and D. Hommel

Appl. Phys. Lett. 101, 022413 (2012); http://dx.doi.org/10.1063/1.4734761 (4 pages)

Online Publication Date: 13 July 2012

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We report on the fabrication of pseudomorphic wurtzite Ga1−xMnxN grown on GaN with Mn concentrations up to 10% using molecular beam epitaxy. According to Rutherford backscattering, the Mn ions are mainly at the Ga-substitutional positions, and they are homogeneously distributed according to depth-resolved Auger-electron spectroscopy and secondary-ion mass-spectroscopy measurements. A random Mn distribution is indicated by transmission electron microscopy, and no Mn-rich clusters are present for optimized growth conditions. A linear increase of the c-lattice parameter with increasing Mn concentration is found using x-ray diffraction. The ferromagnetic behavior is confirmed by superconducting quantum-interference measurements showing saturation magnetizations of up to 150 emu/cm3.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.05.Ea III-V semiconductors
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.ag Semiconductors
75.50.Pp Magnetic semiconductors

Perpendicular-anisotropy CoFeB-MgO magnetic tunnel junctions with a MgO/CoFeB/Ta/CoFeB/MgO recording structure

H. Sato, M. Yamanouchi, S. Ikeda, S. Fukami, F. Matsukura, and H. Ohno

Appl. Phys. Lett. 101, 022414 (2012); http://dx.doi.org/10.1063/1.4736727 (4 pages) | Cited 2 times

Online Publication Date: 13 July 2012

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We investigated perpendicular CoFeB-MgO magnetic tunnel junctions (MTJs) with a recording structure consisting of two CoFeB-MgO interfaces, MgO/CoFeB (1.6 nm)/Ta (0.4 nm)/CoFeB (1.0 nm)/MgO. Thermal stability factor of MTJ with the structure having junction size of 70 nmφ was increased by a factor of 1.9 from the highest value of perpendicular MTJs with single CoFeB-MgO interface having the same device structure. On the other hand, intrinsic critical current for spin transfer torque switching of the double- and single-interface MTJs was comparable.
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75.30.Gw Magnetic anisotropy
75.50.Ss Magnetic recording materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.Mk Spin transport through interfaces

Spin relaxation mechanism in silver nanowires covered with MgO protection layer

H. Idzuchi, Y. Fukuma, L. Wang, and Y. Otani

Appl. Phys. Lett. 101, 022415 (2012); http://dx.doi.org/10.1063/1.4737001 (4 pages) | Cited 2 times

Online Publication Date: 13 July 2012

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Spin-flip mechanism in Ag nanowires with MgO surface protection layers has been investigated by nonlocal spin injection using permalloy/Ag lateral spin valves. The spin flip events mediated by surface scattering are effectively suppressed by the MgO capping layer. The spin relaxation process was found to be well described in the framework of Elliott-Yafet mechanism (R. J. Elliott, Phys. Rev. 96, 266 (1954); Y. Yafet, in Solid State Physics, edited by F. Seitz and D. Turnbull (Academic, New York, 1963), pp. 1–98) and then the probabilities of spin-filp scattering for phonon or impurity mediated momentum scattering is precisely determined in the nanowires. The temperature dependent spin-lattice relaxation follows the Bloch-Grüneisen theory (V. F. Bloch, Z. Phys. 59, 208 (1930); V. E. Grüneisen, Ann. Phys. 5, 530 (1933)) and falls on to a universal curve of Ag as in the conduction-electron-spin resonance data for bulk.
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72.25.Rb Spin relaxation and scattering
73.25.+i Surface conductivity and carrier phenomena
81.65.-b Surface treatments
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
72.25.Ba Spin polarized transport in metals

Manipulating spin injection into organic materials through interface engineering

F. J. Yue, Y. J. Shi, B. B. Chen, H. F. Ding, F. M. Zhang, and D. Wu

Appl. Phys. Lett. 101, 022416 (2012); http://dx.doi.org/10.1063/1.4737008 (4 pages) | Cited 1 time

Online Publication Date: 13 July 2012

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The correlation of spin injection efficiency and interfacial resistance is investigated in La0.67Sr0.33MnO3 (LSMO)/Alq3/Co organic spin-valve devices. When a thin layer of copper phthalocyanine (CuPc) is inserted between LSMO and Alq3, the magnetoresistance (MR) of the device decrease to only ∼0.4% at 50 K, in sharp contrast to ∼6% MR ratio at the same bias voltage for the device without CuPc interlayer. Meanwhile, the electrical resistance decreases by one order of magnitude, indicating that the interface barrier height is reduced. These results reflect that a strong correlation between the significant decrease of spin injection efficiency at LSMO/CuPc interface and the reduced interfacial resistance. The findings indicate that the conductivity mismatch problem is applicable to organic materials and the interfacial resistance has important impact on the spin injection efficiency.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Network analyzer measurements of spin transfer torques in magnetic tunnel junctions

Lin Xue, Chen Wang, Yong-Tao Cui, J. A. Katine, R. A. Buhrman, and D. C. Ralph

Appl. Phys. Lett. 101, 022417 (2012); http://dx.doi.org/10.1063/1.4737017 (4 pages) | Cited 2 times

Online Publication Date: 13 July 2012

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We demonstrate a simple network-analyzer technique to make quantitative measurements of the bias dependence of spin torque in a magnetic tunnel junction. We apply a microwave current to exert an oscillating spin torque near the ferromagnetic resonance frequency of the tunnel junction’s free layer. This produces an oscillating resistance that, together with an applied direct current, generates a microwave signal that we measure with the network analyzer. An analysis of the resonant response yields the strength and direction of the spin torque at non-zero bias. We compare to measurements of the spin torque vector by time-domain spin-torque ferromagnetic resonance.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
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Identifying capacitive and inductive loss in lumped element superconducting hybrid titanium nitride/aluminum resonators

Michael R. Vissers, Martin P. Weides, Jeffrey S. Kline, Martin Sandberg, and David P. Pappas

Appl. Phys. Lett. 101, 022601 (2012); http://dx.doi.org/10.1063/1.4730389 (5 pages) | Cited 3 times

Online Publication Date: 9 July 2012

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We present a method to systematically locate and extract capacitive and inductive losses in superconducting resonators at microwave frequencies by use of mixed-material, lumped element devices. In these devices, ultra-low loss titanium nitride was progressively replaced with aluminum in the inter-digitated capacitor and meandered inductor elements. By measuring the power dependent loss at 50 mK as the Al/TiN fraction in each element is increased, we find that at low electric field, i.e., in the single photon limit, the loss is two level system in nature and is correlated with the amount of Al capacitance rather than the Al inductance. In the high electric field limit, the remaining loss is linearly related to the product of the Al area times its inductance and is likely due to quasiparticles generated by stray IR radiation. At elevated temperature, additional loss is correlated with the amount of Al in the inductance, with a power independent TiN-Al interface loss term that exponentially decreases as the temperature is reduced. The TiN-Al interface loss is vanishingly small at the 50 mK base temperature.
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85.25.-j Superconducting devices
84.32.Tt Capacitors

Nonlinear induction detection of electron spin resonance

Gil Bachar, Oren Suchoi, Oleg Shtempluck, Aharon Blank, and Eyal Buks

Appl. Phys. Lett. 101, 022602 (2012); http://dx.doi.org/10.1063/1.4734500 (4 pages)

Online Publication Date: 12 July 2012

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We present an approach to the induction detection of electron spin resonance (ESR) signals exploiting the nonlinear properties of a superconducting resonator. Our experiments employ a yttrium barium copper oxide superconducting stripline microwave (MW) resonator integrated with a microbridge. A strong nonlinear response of the resonator is thermally activated in the microbridge when exceeding a threshold in the injected MW power. The responsivity factor characterizing the ESR-induced change in the system’s output signal is about 100 times larger when operating the resonator near the instability threshold, compared to the value obtained in the linear regime of operation. Preliminary experimental results, together with a theoretical model of this phenomenon are presented. Under appropriate conditions, nonlinear induction detection of ESR can potentially improve upon the current capabilities of conventional linear induction detection ESR.
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76.30.-v Electron paramagnetic resonance and relaxation
85.25.-j Superconducting devices
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Magnetoelectric coupling in nanocrystalline Pb0.82La0.18TiO3

Lin Ju, Jifan Hu, Li Sun, Minglei Zhao, Yongjia Zhang, Hongwei Qin, and Liangmo Mei

Appl. Phys. Lett. 101, 022901 (2012); http://dx.doi.org/10.1063/1.4732803 (5 pages) | Cited 1 time

Online Publication Date: 9 July 2012

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The combined effect of Pb vacancies and La dopant can induce ferromagnetism below 75 K for Pb0.82La0.18TiO3 plates annealed at 700,1000, and 1200 °C for 1 h. Pb0.82La0.18TiO3 plates annealed at 1000 °C for 1 h show the coexistence of ferromagnetism resulting from oxygen vacancies at/near surfaces of nanograins and ferroelectricity near room temperature. Under application of magnetic field, the dielectric constant decreases and the ferroelectric transition temperature shifts to high temperature for Pb0.82La0.18TiO3 multiferroic plates. In addition, the electric field treatment leads to an enormous enhancement of saturation magnetization for Pb0.82La0.18TiO3 multiferroic plates, showing a strong magnetoelectric coupling.
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75.85.+t Magnetoelectric effects, multiferroics
77.80.B- Phase transitions and Curie point
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.22.Ch Permittivity (dielectric function)
61.72.jd Vacancies

Strong enhancement of magnetoelectric coupling in Dy3+ doped HoMnO3

J. Magesh, P. Murugavel, R. V. K. Mangalam, K. Singh, Ch. Simon, and W. Prellier

Appl. Phys. Lett. 101, 022902 (2012); http://dx.doi.org/10.1063/1.4733367 (4 pages) | Cited 2 times

Online Publication Date: 9 July 2012

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The magnetoelectric effect in Ho0.9Dy0.1MnO3 is found 31 times stronger than HoMnO3 which could be due to strong lattice frustration arises out of the structural distortion on doping. The TN observed from magnetic measurement reveals a double peak corresponding to the in-plane and inter-planar ordering leading to assignment of Γ4 structure. The antiferromagnetic transition at TN indeed drives dielectric transition mediated by the lattice strain whereas at the TSR, lattice strain drives the spin reorientation of Mn3+. In contrary to the long held belief, the magnetic structure changes from Γ4 to Γ1 at TSR instead of Γ4 to Γ3.
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75.85.+t Magnetoelectric effects, multiferroics
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Ds Spin waves
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
81.40.Lm Deformation, plasticity, and creep

Ultralow equivalent magnetic noise in a magnetoelectric Metglas/Mn-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure

Yaojin Wang, Junqi Gao, Menghui Li, D. Hasanyan, Ying Shen, Jiefang Li, D. Viehland, and Haosu Luo

Appl. Phys. Lett. 101, 022903 (2012); http://dx.doi.org/10.1063/1.4733963 (4 pages) | Cited 3 times

Online Publication Date: 10 July 2012

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An ultralow equivalent magnetic noise of 6.2 pT/√Hz at 1 Hz was obtained in a bimorph heterostructure sensor unit consisting of longitudinal-magnetized Metglas layers and a transverse-poled 1 mol. % Mn-doped Pb(Mg1/3Nb2/3)O3-29PbTiO3 (PMN-PT) single crystal. Furthermore, the equivalent magnetic noise was ≤1 pT/√Hz at 10 Hz. Compared with previously reported multi-push-pull configuration Metglas/PMN-PT sensor units, the current heterostructure exhibits a higher magnetoelectric coefficient of 61.5 V/(cm × Oe), a similar equivalent magnetic noise at 1 Hz and a lower noise floor at several hertz range. The ultralow equivalent magnetic noise in this sensor unit is due to the low tangent loss and ultrahigh piezoelectric properties of Mn-doped PMN-PT single crystals.
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77.55.Nv Multiferroic/magnetoelectric films
75.85.+t Magnetoelectric effects, multiferroics
77.65.-j Piezoelectricity and electromechanical effects
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Negative capacitance induced by redistribution of oxygen vacancies in the fatigued BiFeO3-based thin film

Qingqing Ke, Xiaojie Lou, Haibo Yang, Amit Kumar, Kaiyang Zeng, and John Wang

Appl. Phys. Lett. 101, 022904 (2012); http://dx.doi.org/10.1063/1.4733982 (4 pages) | Cited 1 time

Online Publication Date: 10 July 2012

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The capacitance dispersion in La and Mg co-substituted BiFeO3 thin film has been studied at different stages of polarization switching. A negative capacitance (NC) behavior is observed in the sample that is fatigued above 109 switching cycles. The origin of the NC is investigated through analyzing relaxation processes and charge transport kinetics by admittance spectroscopy. An activation energy of ∼0.6 eV and a zero field mobility μ0 = 5.33±0.02×10−13m2/Vs are thus obtained. A physical mechanism is proposed to explain this behavior. It involves a redistribution of oxygen vacancies, which are trapped at the film/electrode interface during the fatigue process.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
61.72.jd Vacancies
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
77.22.Gm Dielectric loss and relaxation
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.me Fatigue

Controlled growth of epitaxial BiFeO3 films using self-assembled BiFeO3-CoFe2O4 multiferroic heterostructures as a template

Yanxi Li, Yaodong Yang, Jianjun Yao, Ravindranath Viswan, Zhiguang Wang, Jiefang Li, and D. Viehland

Appl. Phys. Lett. 101, 022905 (2012); http://dx.doi.org/10.1063/1.4734508 (5 pages) | Cited 2 times

Online Publication Date: 11 July 2012

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The growth mechanism of a BiFeO3 layer deposited on self assembled (0.65) BiFeO3-(0.35) CoFe2O4 (BFO-CFO) composite thin films was studied. Epitaxial and self-assembled BFO-CFO thin films were deposited on SrTiO3 (111) substrates by pulsed laser deposition and were subsequently used as a seed layer for the deposition of an additional BFO layer. x-ray line scans showed the heterostructures were highly epitaxial. Cross-sectional scanning electron microscopy and focused ion beam images revealed the top BFO layer grew preferentially from BFO nanopillars in the BFO-CFO thin films, thus, demonstrating controlled growth. The multiferroic properties of this new nanostructure were then studied.
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81.16.Dn Self-assembly
81.16.Mk Laser-assisted deposition
77.55.Nv Multiferroic/magnetoelectric films
81.15.Fg Pulsed laser ablation deposition

Tunneling electroresistance effect in Pt/MgO/Pt/PbTiO3/Pt ferroelectric tunnel junctions

Zhijun Ma, Tianjin Zhang, Ruikun Pan, Kun Liang, Duofa Wang, Jingang Wang, Jinzhao Wang, Juan Jiang, Yajun Qi, and Huifang Chu

Appl. Phys. Lett. 101, 022906 (2012); http://dx.doi.org/10.1063/1.4734513 (5 pages)

Online Publication Date: 11 July 2012

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Tunneling electroresistance (TER) effect was investigated in Pt/MgO/Pt/PbTiO3/Pt ferroelectric tunnel junctions (FTJs) theoretically. Compared to Pt/MgO/PbTiO3/Pt FTJs with the same composite barrier thickness (unit cells), FTJs with a thicker Pt interlayer (2 ∼ 3 unit cells) could provide 1 ∼ 6 orders of magnitude improvement in the TER ratio in a wide range of polarization. Resonant tunneling effect and/or enhanced asymmetry of the potential energy profile induced by the resonant-tunneling structure of MgO/Pt/PbTiO3 in Pt/MgO/Pt/PbTiO3/Pt FTJs is responsible for the TER improvement.
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73.40.Rw Metal-insulator-metal structures
77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity

Differential scanning calorimeter and infrared imaging for electrocaloric characterization of poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer

Gael Sebald, Laurence Seveyrat, Jean-Fabien Capsal, Pierre-Jean Cottinet, and Daniel Guyomar

Appl. Phys. Lett. 101, 022907 (2012); http://dx.doi.org/10.1063/1.4734924 (3 pages) | Cited 1 time

Online Publication Date: 12 July 2012

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Electrocaloric properties of poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer were determined by two methods. A modified differential scanning calorimeter measures the entropy variation when applying an electric field under isothermal conditions. Alternative technique consists of an infrared imaging camera that gives direct information on temperature variation in pseudo-adiabatic condition. Both techniques give similar results with a heat capacity of 1500 J/(kg K). For an electric field of 80 V/μm, entropy variation was measured at 15.1 J/(kg K) and a temperature variation of 2.75 K. High frequency measurement is possible using infrared imaging, and a strong frequency dependence of the electrocaloric effect was observed.
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77.70.+a Pyroelectric and electrocaloric effects
77.55.Kt Pyroelectric films
42.79.Pw Imaging detectors and sensors
61.41.+e Polymers, elastomers, and plastics

Enhanced magnetoelectric effect in self-stressed multi-push-pull mode Metglas/Pb(Zr,Ti)O3/Metglas laminates

Menghui Li, Yaojin Wang, Junqi Gao, Jiefang Li, and D. Viehland

Appl. Phys. Lett. 101, 022908 (2012); http://dx.doi.org/10.1063/1.4737179 (3 pages) | Cited 3 times

Online Publication Date: 13 July 2012

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Two methods to effectively induce self-stress on Metglas/Pb(Zr,Ti)O3/Metglas laminate are presented: (i) applying a dc magnetic field to the Metglas layers or (ii) applying a dc electric field to the core piezoelectric composites. An optimum self-stress enhances the magnetoelectric (ME) effect in the laminates. With a 20 Oe dc magnetic bias, the value of αME for the self-stressed laminate was enhanced to 31.4 V/cm · Oe, which was by a factor of 1.24× compared to the laminate without self-stress. Furthermore, the equivalent magnetic noise floor was reduced by the self-stress at low frequencies.
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75.85.+t Magnetoelectric effects, multiferroics
77.55.Nv Multiferroic/magnetoelectric films
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Polarization conversion with elliptical patch nanoantennas

Feng Wang, Ayan Chakrabarty, Fred Minkowski, Kai Sun, and Qi-Huo Wei

Appl. Phys. Lett. 101, 023101 (2012); http://dx.doi.org/10.1063/1.4731792 (4 pages) | Cited 8 times

Online Publication Date: 9 July 2012

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In this paper, we demonstrate arrays of optical patch nanoantennas can convert light polarization through reflection. By breaking the azimuthal symmetry, elliptical plasmonic patch nanoantennas exhibit both even and odd cavity modes, which can be expressed by Mathieu functions. It is shown that by properly orienting the incident polarization, a linearly polarized light in resonance with one cavity mode can be converted into an elliptical or circular polarization after reflection. Since the major cavity modes can be excited at all incident angles, the polarization conversion by these elliptical patch nanoantennas can be realized with wide range of incident angles.
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84.40.Ba Antennas: theory, components and accessories

Towards spin injection from silicon into topological insulators: Schottky barrier between Si and Bi2Se3

C. Ojeda-Aristizabal, M. S. Fuhrer, N. P. Butch, J. Paglione, and I. Appelbaum

Appl. Phys. Lett. 101, 023102 (2012); http://dx.doi.org/10.1063/1.4733388 (4 pages) | Cited 2 times

Online Publication Date: 9 July 2012

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A scheme is proposed to electrically measure the spin-momentum coupling in the topological insulator surface state by injection of spin polarized electrons from silicon. As an initial approach, devices were fabricated consisting of thin (<100 nm) exfoliated crystals of Bi2Se3 on n-type silicon with independent electrical contacts to silicon and Bi2Se3. Analysis of the temperature dependence of thermionic emission in reverse bias indicates a barrier height of 0.34 eV at the Si-Bi2Se3 interface. This robust Schottky barrier opens the possibility of original device designs based on sub-band gap internal photoemission from Bi2Se3 into Si.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
79.40.+z Thermionic emission
79.60.-i Photoemission and photoelectron spectra
72.25.-b Spin polarized transport

Photoinduced conductance switching in a dye-doped gold nanoparticle transistor

Makoto Yamamoto, Toshifumi Terui, Rieko Ueda, Keisuke Imazu, Kaoru Tamada, Takeshi Sakano, Kenji Matsuda, Hisao Ishii, and Yutaka Noguchi

Appl. Phys. Lett. 101, 023103 (2012); http://dx.doi.org/10.1063/1.4733612 (4 pages)

Online Publication Date: 9 July 2012

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Photoinduced conductance switching was demonstrated in a copper phthalocyanine (CuPc)-doped gold nanoparticle (GNP) transistor formed in a nanogap electrode with a back gate structure. Two specific states were reversibly induced in conductance of the CuPc-doped devices by light irradiation and applied voltages. The probability of occurrence of conductance switching decreased with a reduction in the number of incident photons. In addition, conductance switching was not observed in the devices before CuPc doping. Conductance switching originates from change in the local potential of GNPs, possibly induced by a charge-state bistability of an individual CuPc molecule worked as a floating gate.
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85.35.Gv Single electron devices

Altering regularities of electronic transport properties in twisted graphene nanoribbons

G. P. Tang, J. C. Zhou, Z. H. Zhang, X. Q. Deng, and Z. Q. Fan

Appl. Phys. Lett. 101, 023104 (2012); http://dx.doi.org/10.1063/1.4733618 (5 pages) | Cited 1 time

Online Publication Date: 9 July 2012

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Based on density-function theory combined with nonequilibrium Green’s function method, the electronic transport properties of twisted armchair- and zigzag-edge graphene nanoribbons (AGNRs and ZGNRs) are investigated. Results show that electronic transport properties are sensitive to twisting deformations for semiconductor-type AGNRs, but are robust against twisting deformations for quasi-metallic AGNRs and ZGNRs. The electronic conduction becomes weaker gradually for moderate-gap semiconductor-type AGNRs, but gets stronger for wide-gap semiconductor-type AGNRs when the twisted angle increases to 120°. While for quasi-metallic AGNRs and ZGNRs, the electronic conduction is strong and obeys Ohm’s law of resistance strictly. Mechanisms for such results are suggested.
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72.80.Vp Electronic transport in graphene

Confinement of vacancies during annealing of H implanted GaN sandwiched between two {InGaN/GaN} superlattices

N. Cherkashin, A. Claverie, D. Sotta, J.-M. Bethoux, L. Capello, and O. Kononchuk

Appl. Phys. Lett. 101, 023105 (2012); http://dx.doi.org/10.1063/1.4733619 (5 pages)

Online Publication Date: 9 July 2012

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Using transmission electron microscopy techniques, we identify the extended defects of interstitial and vacancy types found after H implantation and annealing in GaN. We statistically analyze the effect of boarding or sandwiching GaN between strained superlattices on these populations of defects. We finally demonstrate the possibility to use compressively strained layers to localize and favour the precipitation of vacancy type defects in GaN. The source of excess vacancies, the mechanism responsible for the cavity localization, and the drastic increase of their volume fraction are discussed.
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61.72.jd Vacancies
61.72.Cc Kinetics of defect formation and annealing
61.72.U- Doping and impurity implantation
81.30.Mh Solid-phase precipitation

Growth and photoluminescence of InxGa1−xAs quantum dots on the surface of GaAs nanowires by metal organic chemical vapor deposition

Xin Yan, Xia Zhang, Xiaomin Ren, Junshuai Li, Xiaolong Lv, Qi Wang, and Yongqing Huang

Appl. Phys. Lett. 101, 023106 (2012); http://dx.doi.org/10.1063/1.4734391 (4 pages) | Cited 1 time

Online Publication Date: 10 July 2012

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InxGa1−xAs (x = 0.6-1) quantum dots are grown on the {112} side facets of GaAs nanowires by metal organic chemical vapor deposition. The emission spectrum of quantum dots exhibits a multi-peak structure due to size and composition fluctuations. The emission wavelength of quantum dots ranges from 857 nm to 930 nm at 77 K, which is distinctly blueshifted relative to that on traditional GaAs (100) planar substrate. The emission linewidth of an ensemble of quantum dots increases from 29.5 meV to 40.5 meV with increasing the In content, indicating a broader composition distribution of quantum dots.
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81.07.Ta Quantum dots
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
81.05.Ea III-V semiconductors

Ternary eutectic growth of nanostructured thermoelectric Ag-Pb-Te materials

Hsin-jay Wu, Wei-jian Foo, Sinn-wen Chen, and G. Jeffrey Snyder

Appl. Phys. Lett. 101, 023107 (2012); http://dx.doi.org/10.1063/1.4733661 (4 pages) | Cited 1 time

Online Publication Date: 10 July 2012

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Nanostructured Ag-Pb-Te thermoelectric materials were fabricated by unidirectionally solidifying the ternary Ag-Pb-Te eutectic and near-eutectic alloys using the Bridgeman method. Specially, the Bridgman-grown eutectic alloy exhibited a partially aligned lamellar microstructure, which consisted of Ag5Te3 and Te phases, with additional 200-600 nm size particles of PbTe. The self-assembled interfaces altered the thermal and electronic transport properties in the bulk Ag-Pb-Te eutectic alloy. Presumably due to phonon scattering from the nanoscale microstructure, a low thermal conductivity (κ = 0.3 W/mK) was achieved of the eutectic alloy, leading to a zT peak of 0.41 at 400 K.
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81.16.Dn Self-assembly
81.30.Fb Solidification
72.15.Jf Thermoelectric and thermomagnetic effects
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
63.22.Kn Clusters and nanocrystals
81.05.Bx Metals, semimetals, and alloys

Thickness dependence oscillations of transport properties in thin films of a topological insulator Bi91Sb9

E. I. Rogacheva, D. S. Orlova, O. N. Nashchekina, M. S. Dresselhaus, and S. Tang

Appl. Phys. Lett. 101, 023108 (2012); http://dx.doi.org/10.1063/1.4730950 (4 pages)

Online Publication Date: 11 July 2012

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The dependences of the electrical conductivity, Hall coefficient, magnetoresistance, and Seebeck coefficient on the thickness d (d = 15–400 nm) of the topological insulator Bi91Sb9 thin films grown on mica substrates were obtained at room temperature. In addition to the oscillations with a period Δd = (105 ± 5) nm in the thickness range d = 100–400 nm which are attributed to the quantization of the semiconductor electron energy spectrum, oscillations with a period Δd = (8 ± 2) nm in the range d = 15–60 nm were also revealed. It is suggested that the existence of the high-frequency oscillations in the thin films may be connected with the quantization of the metallic surface states energy spectrum.
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73.61.At Metal and metallic alloys
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Pa Thermoelectric and thermomagnetic effects
73.43.Qt Magnetoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Lw Thermoelectric effects

Emission aperture size limited the guided mode extraction characteristics of GaN-based ultrathin-film photonic crystal micro-light-emitting diodes

Chun-Feng Lai

Appl. Phys. Lett. 101, 023109 (2012); http://dx.doi.org/10.1063/1.4734509 (4 pages)

Online Publication Date: 11 July 2012

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This study experimentally and theoretically investigated individual GaN-based ultrathin-film micro-light-emitting diodes (μ-uTFLEDs) with photonic crystal (PhC) nanostructures of varying emission aperture sizes from 5 to 100 μm. High-resolution angular-spectra-resolved electroluminescence measurements revealed the guided mode extraction characteristics that dependence on the emission aperture size. Experimental results indicate that the different diffraction vectors of guided modes have varying extraction lengths; therefore, the emission aperture size acts as a gradual guided mode filter. This effect also limits the suitability of GaN PhC μ-uTFLEDs for the optical engine in pico-projectors.
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85.60.Jb Light-emitting devices

Structural characterization of CdSe/ZnS quantum dots using medium energy ion scattering

M. A. Sortica, P. L. Grande, C. Radtke, L. G. Almeida, R. Debastiani, J. F. Dias, and A. Hentz

Appl. Phys. Lett. 101, 023110 (2012); http://dx.doi.org/10.1063/1.4734686 (4 pages)

Online Publication Date: 11 July 2012

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In the present work, we have analyzed CdSe/ZnS core-shell quantum dots by medium energy ion scattering (MEIS), which is a powerful technique to explore the synthesis, formation, stability, and elemental distribution of such core-shell structures, along with other auxiliary analytical techniques. By comparing different quantum-dot structural models spectra with the experimental MEIS data, we were able to obtain some sample structural information. We found that, despite the well known non stoichiometric Cd:Se ratio, the core is stoichiometric, and there is an excess of cadmium distributed in the shell.
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68.65.Hb Quantum dots (patterned in quantum wells)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.07.Ta Quantum dots
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